1. Field of the Invention
The present invention relates to an inkjet printing apparatus, and more particularly relates to an inkjet printing apparatus which includes a print head having a plurality of ejection ports arranged in a direction intersecting with the direction in which a print medium is conveyed and which ejects ink from the ejection port to perform printing.
2. Description of the Related Art
As one type of inkjet printing apparatus that ejects droplets (ink) from a print head to perform printing, a line head type inkjet printing apparatus is known. The line head type inkjet printing apparatus includes a print head having a plurality of ejection ports arranged and formed in a direction intersecting with the direction in which a print medium is conveyed. With the print medium conveyed in the direction intersecting with the direction in which an ejection port array extends, the droplets are ejected from the ejection ports of the print head on the print medium to perform printing. In the line head type inkjet printing apparatus, droplets used for printing for one line are ejected from the print head at one time, and such printing is continuously performed. Therefore, the line head type inkjet printing apparatus has an advantage in that its printing speed is high.
In this line head type inkjet printing apparatus, printing can be performed on print media having various widths as long as their widths are equal to or less than the length corresponding to the portion where the ejection ports in the print head are formed. However, since the line head type inkjet printing apparatus continuously performs printing on print media having widths that are narrower than the length of the portion where the ejection ports are formed, some of the ejection ports are repeatedly used for the ejecting and some other ejection ports are seldom used for the ejecting.
In general, a printing element that applies energy to liquid stored in a print head to eject droplets from ejection ports has a lifetime, and the number of times the printing element is driven is limited. When the same printing element is continuously driven to continuously eject droplets through the same ejection port, the life of the printing element is shortened. Moreover, when droplets are repeatedly ejected from the same ejection port, it is know that, before the printing element reaches the end of its life, the ejection properties (ejection amount) of droplets ejected from the ejection port are changed. Hence, Japanese Patent Laid-Open No. 2005-297510 discloses an inkjet printing apparatus in which, every predetermined number of sheets printed, a print head is moved in a direction intersecting with the direction in which the print medium is conveyed, and thus ejection ports to be used for printing are changed. This inkjet printing apparatus is used to perform printing, and thus ejection ports used for the printing can be distributed, and the number of times each ejection port is used is made uniform.
However, a case that a large amount of particular type of ink is only consumed, depending on a printed image, can be considered. In this case, a large amount of a particular type of ink is only ejected even though a small number of sheets are printed, and thus a printing element arranged in a print head that ejects the specific type of ink may only be used repeatedly. Here, in the printing apparatus disclosed in Japanese Patent Laid-Open No. 2005-297510, since the print head is not moved because a small number of sheets are printed, the ejection properties of the particular type of ink may be changed. Therefore, when printing is performed on a print medium larger than the print medium that has been used, the density of a specific color may differ between a region corresponding to the width of the print medium on which the printing has been performed and a region outside the above-mentioned region. The occurrence of this density difference may cause the quality of a printed image to be reduced.